Dear Joseph,
I think, you already did the most classical test to determine what is in
your crystal.
Maybe you can try a destructive approach by washing the crystal prior to
put them in Agarose gel do a short run and color with ethydium bromide.
Simpler, you can also melt the crystal after washing them and do some
spectroscopic experiment (measurement at 260 and 280 nm) the ratio will
help ou to know what is in your crystal.
I can add that I frequently obtained crystal of protein-DNA complex with
this type of crystal growing condition (based on relatively small PEG).
Sometimes it was only DNA. And most of the times when it was DNA only,
crystal have a pentagon shape, like certain one on your image.
If you have the opportunity to test diffraction, even at low resolution
to obtain some information (cell params, matthew coeff) it will help you
do decide what to do.
And maybe are they already good enough to do some in-situ data
collection or serial synchrotron experiment.
Hope to help
Nicolas
Nicolas Foos
PhD
Structural Biology Group
European Synchrotron Radiation Facility (E.S.R.F)
71, avenue des Martyrs
CS 40220
38043 GRENOBLE Cedex 9
+33 (0)6 76 88 14 87
+33 (0)4 76 88 45 19
On 19/06/2017 16:20, Joseph Ho wrote:
Dear all:
I would like to seek your opinion on our crystal hits. We are working
on protein/dsDNA complex. By changing different protein and DNA
(14-22bp) constructs, we recently got some hits from commercial
screens using sitting drop vapor diffusion (very small xtals). The
precipitant is PEG and the picture of crystals are attached. In this
particular condition, it is 30%PEG3350, sodium succinate pH5.5 and
100mM NaCl. The crystal seems floating and sit in the bottom. We do
some test shot from other conditions and it is not salt crystals. The
crystals can suck in izit dye. I do some google and it seems izit dye
also turns dsDNA crystal into blue. We also do UV/Vis microscope but
no Trp fluorescence (6 Trp in 256 aa). It may due to low Trp.
This is our first time to work on protein/DNA complex crystals and we
are not certain if this is just DNA or protein/DNA crystals. Can you
provide your comments on our hits?
Thank you for your help
Joseph
